PHYSIOLOGICAL EFFECTS OF MICRONUTRIENT DEFICIENCIES IN ISOLATED ROOTS OF LYCOPERSICUM ESCULENTUM

Abstract

SummaryThis paper describes techniques for the removal of trace element impurities in nutrient reagents without the introduction of toxic residues inhibitory to the growth of excised tomato roots. The zinc requirement of excised roots, hitherto in some doubt, is clearly demonstrated in media treated with dithizone. The three features of growth—main axis extension, lateral initiation and lateral extension—were followed during the onset of, and recovery from, iron, manganese, copper, zinc and molybdenum deficiencies. Symptoms of iron and manganese deficiencies were manifested in the first culture passage; those of copper, zinc and molybdenum in the second passage. In manganese, copper, zinc and molybdenum deficiencies, there was a gradual decline in growth rate, but growth ceased abruptly in iron deficiency. Inhibition of lateral root initiation was more severe in iron and copper deficiencies than in other deficiencies studied. Lateral elongation was stimulated by zinc deficiency and retarded less by manganese than by iron, copper and molybdenum deficiencies. Addition of deficient elements showed that primary and secondary meristems varied in their capacity to recover. Stimulation of lateral initiation occurred when iron and zinc were added to deficient cultures and lateral elongation was stimulated in manganese recovery experiments. Protracted periods in iron, manganese, copper and zinc deficient media caused degeneration of root tissues, but recovery was still possible in roots maintained without molybdenum for 28 days. Results are discussed in relation to possible predominant roles for the five trace elements in determining the pattern of growth of excised tomato roots. Response to these elements was not uniform in the root and it is clear that cellular differentiation is an important factor in trace element requirement and control of growth.